Vitamin C (VC) and Vitamin B9 (VB9) are essential micronutrients integral to numerous biological functions and critical for maintaining human health. The rapid detection of these vitamins is important for verifying nutritional supplements and aiding in clinical diagnoses. This study combined terahertz time-domain spectroscopy (THz-TDS) with metasurface technology to develop a fast, sensitive, and non-destructive detection method for VC and VB9. Firstly, we determined the characteristic absorption peaks and molecular vibration modes of VC and VB9 within the 0.5–4.0 THz range through quantum chemical calculation and THz-TDS measurement. Then, we designed and fabricated a metasurface biosensor to match its resonance peak with the communal peak of VC and VB9, enhancing the interaction between THz waves and these vitamins. Using this biosensor, we analyzed solutions with different concentrations of VC and VB9. An increase in vitamin concentrations resulted in frequency shifts in the THz resonance peak. Quantifiable relationships between frequency shifts and the vitamin concentrations were established. The detection limits achieved were 158.82 ng/µL for VC and 353.57 ng/µL for VB9, respectively. This method not only demonstrates high sensitivity but also simplifies the operational process, offering an innovative tool for applications in food safety monitoring and clinical diagnostics.

Industrial solid waste refers to the solid waste that is produced in industrial production activities. Without correct treatment and let-off, industrial solid waste may cause environmental pollution due to a variety of pollutants and toxic substances that are contained in it. Conventional detection methods for identifying harmful substances are high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS), which are complicated, time-consuming, and highly demanding for the testing environment. Here, we propose a method for the quantitative analysis of harmful components in industrial solid waste by using terahertz (THz) spectroscopy combined with chemometrics. Pyrazinamide, benazepril, cefprozil, and bisphenol A are four usual hazardous components in industrial solid waste. By comparing with the Raman method, the THz method shows a much higher accuracy for their concentration analysis (90.3–99.8% vs. 11.7–86.9%). In addition, the quantitative analysis of mixtures was conducted, and the resulting prediction accuracy rate was above 95%. This work has high application value for the rapid, accurate, and low-cost detection of industrial solid waste.

In this paper, we proposed a polarization-independent terahertz surface plasmon resonance (SPR) biosensor based on an angular cyclic element structure. The biosensor has the advantages of high sensitivity detection and high stability against the polarization change of incident terahertz light. Based on the principle that the spatial longitudinal electric field of the SPR biosensor is nonlinear and sensitive to the dielectric constant of the sample, we theoretically proved that specific nonlinear response curves with certain saturating speed and amplitude can be formed to identify different samples. The biosensor was applied to identify Panax (notoginseng, ginseng and American ginseng, 48 samples each) and Paeonia (white peony and red peony, 48 samples each) with the accuracy of 95.8% and 94.4%, respectively. The standard deviations (SD) were less than 0.347% and 0.403%, respectively. Therefore, the polarization-independent terahertz biosensor can rapidly and accurately identify Panax species and Paeonia species. These results provide a new reference for rapid and low-cost identification of medicine species.

Pharmaceutical quality control plays a critical role in safeguarding patient safety and ensuring therapeutic efficacy. However, conventional analytical methods are often hindered by laborious procedures and complex chemical preparation requirements. This study presents a rapid, non-destructive pharmaceutical analysis approach by introducing terahertz spectroscopy for the dual-parametric detection of the anticoagulant warfarin. Characteristic absorption peaks of warfarin within the 4–10 THz range were experimentally identified and theoretically resolved through density functional theory calculations, employing both single-molecule and unit cell models. Furthermore, three strong absorption peaks were selected to construct multivariate regression models correlating spectral parameters (peak intensity and area) with warfarin weight, achieving a detection limit of 0.641 mg within a 5 min analytical workflow. This approach enables simultaneous molecular fingerprint identification and quantitative determination without chemical modification, meeting the requirements for the rapid screening of active pharmaceutical ingredients.